Project Summary Most of the studies on epigenetic inheritance focus on the identification of sperm-borne factors that carry the epigenetic memory and how they act on the epigenome/genome of the embryos so that the specific epigenetic memory can be recalled and manifested as a specific phenotype in offspring. However, one fundamental question remains unanswered: given that the effects of exposures, either environmental or dietary, are presumably initially manifested as epigenetic changes in directly exposed somatic cells (e.g. pancreatic islet cells, adipocytes, hepatocytes, etc.), how do the phenotype-specific epimutations in somatic cells get transduced into spermatozoa? Using a highly reproducible mouse model for intergenerational epigenetic inheritance of a high fat diet (HFD)-induced metabolic disorders, we here propose a series of experiments to tackle this critical question. Our central hypothesis is that HFD- induced epimutations in somatic cells can lead to production of specific sncRNAs that are either encapsulated in extracellular vesicles (EVs), or present as mobile RNAs, which act as the carrier of epigenetic memory once internalized by spermatozoa through either 1) the intra-testicular mechanism (i.e., Sertoli cell HDF-specific epigenetic information transmitted to all developing male germ cells or directly to spermatozoa during spermatogenesis in the testis), or 2) the post-testicular pathway (i.e., HFD-specific epigenetic information transmitted from male reproductive tract epithelial cells to spermatozoa), or 3) a combination of both. To test our hypothesis, we propose to identify when and where male germ cells gain the ability to transmit the HDF-induced metabolic disorder phenotype (Aim1), to study how the intra-testicular pathway contributes to the HFD-specific sperm epigenome (Aim2), to study how the post-testicular pathway influences HFD-specific sperm epigenome (Aim3). Data to be obtained will help fill the knowledge gap in our understanding of the molecular mechanisms underlying the intergenerational epigenetic inheritance of paternally acquired traits in general.